The invention relates to displaying non-linear media data, i.e., digitized audio and video data.
Non-linear media data is audio and video data recorded on a linear medium, e.g., a VHS videotape cassette, and stored in digitized form on a computer storage device, e.g., a hard disk drive. Typically, linear audio data is recorded with a "pulse" equal to the speed at which the linear video data is recorded. That is, if the video data is recorded at 30 frames per second (fps), the accompanying audio data is likewise recorded at 30 fps. This is obviously the case where the audio and video data are recorded simultaneously on a single medium, e.g., a single videotape cassette. However, the recording of the audio data can be distinct from the recording of the video data, e.g, a soundtrack can be recorded in London and a film clip can be shot on location in the Sahara Desert, in which case the speed of recording the video and the audio may or may not be equal. In addition, the standard speeds for filming video and recording audio vary from country to country. For example, the standard speed for recording video in the United States is 30 fps, while the standard speed in Europe is 24 fps. Likewise, the audio sampling rate standard is 22 kHz, but 44 kHz is also used. Thus, in cases where the speeds are different, the two recordings (often referred to as media "channels") must be effectively combined and displayed so that there are no visible or audible gaps or overlaps.
As noted above, the speed at which video data is recorded and displayed can vary, e.g., from 30 fps to 24 fps. Video data from different countries, however, can be successfully edited together and played at a single speed because the human eye cannot detect subtle variations in the number of frames per second. The human ear, however, can detect even subtle variations in the speed at which audio data is played. These variations appear as audible clicks, silences, or other distortions. Over time, differences in the speed at which the video data is displayed and the audio data are played results in visibly and audibly mismatched video and audio data.